I am hoping to produce a circuit that allows for up to 5 low voltage, low output (perhaps a short LED rope light) to run from a single CR123 or 2xAA. I could potentially use 2xCR123 at a push.

I have seen some 555 dimming circuits, along with the LM338 being suggested.

How could I make an efficient, dimming circuit that will provide the most efficient output / longest battery life?

 

How long do you need them to last?
Do you need real "dimming" based on some type of input or do you just mean to have them be dim as to not draw as much power?

 

What type of LED? Typical Vf? Rated max current?